An optical disk or a magneto-optical disk which uses an optical or magneto-optical signal recording system has recently been developed, and an optical recording and reproducing apparatus for recording and reproducing information to and from such a disk has also been developed. In such an apparatus, a tracking actuator is driven in accordance with a polarity and a level of a tracking error signal produced by an optical pickup to attain tracking control so that a track center is always followed without regard to an eccentricity of the disk.
On the other hand, in order to improve a data transfer speed from the disk to a processor, the rotation speed of the disk is increased and a relative speed between a light beam and the track has been increased in spite of the reduction of the eccentricity of the disk. If the relative speed is lower than a pull-in speed determined by a tracking control band, the light beam is pulled onto, a target track but if it is higher than the pull-in speed, the pull-in is unstable and the light beam may be pulled onto a different track. As a result, in an access operation which requires a jump over tracks, the light beam may be pulled onto a track which is far distant from the target track and reaccess operation is needed. Thus, an access time is long.
JP-A-63-181179 discloses a solution to the above problems.
In the disclosed method, tracking is properly attained when amplitudes of a tracking error signal and a tracking sum signal are equal, but the waveform amplitudes are not equal in a disk in which a track groove depth varies. Thus, the disclosed method is not applicable to such a disk.
In the disclosed method, an allowable range for the pull-in to the target track is .vertline.X.vertline.&lt;P/2 when P is a track pitch and X is a deviation of the light beam in a radial direction, measured from the target track. Thus, the pull-in to the target track is not attained when .vertline.X.vertline.&gt;P/2. (X represents an absolute value of X).